Early in their development, ovarian follicles enter a vitellogenic phase that entails the deposition in the oocyte of a yolk mass embedded in an RNA-rich cytoplasm. There is evidence that control of this important phase of development entails the setting of homeostatic levels of cytoplasmic free Ca2+ and cAMP, two widely recognized internal regulators of cellular processes. This proposal is for a physiological and biochemical analysis of how the levels of Ca2+ and cAMP are set, with how they change during the onset and termination of vitellogenesis, and with how they in turn affect two major aspects of oocyte function--vitellogenin uptake from the hemolymph and the relegation of all egg RNA synthesis to the nurse cells. In many dipteran and hemipteran disease vectors the vitellogenic phase of development is triggered by the blood meal that nourishes egg formation. In Hyalophora cecropia it occurs spontaneously as a part of metamorphosis, but the large size and number of follicles make their biochemistry and physiology much more accessible to analysis. Vitellogenin uptake, the suppression of transcription in the oocyte, and the point of insertion of these two processes into the sequence of other events entailed in egg formation are virtually identical among these insects. Studying intracytoplasmic regulation by Ca2+ and cAMP in Hyalophora follicles would therefore yield insights that will be applicable to all insects with nurse cells.